I've been researching wilwood options. Here is a guy that did it and documented it pretty well. He modded a mini and a honda kit to fit.
It looks like both the Mini kits and Honda kits can be modded pretty easily to make them work. Absolute max rotor size on 15's is 11.75 depending on the caliper and wheel offsets. 11 is pretty easy. A couple of kits worth looking at are Wilwood 140-8695 and 140-10736. The mini cooper kit is 140-8740.
The first is an 11" kit using the regular forged dynalite 4 piston caliper. Pads are about the same size as the Miata pad. Lot's of options for pads for them, it's a popular pattern. Hawk blues, porterfields and more are around $65 an axle! Of course carbotechs are double that. Lots of choices though. Best price found was $545.
The second is a Honda kit uses the new Dynapro 6 piston caliper. The hat is a more common 8x7 disc bolt pattern so the discs are more plentiful. The included disc is 12.19" too large in my book but it would be easy to sell them off and get a proper size 11.75 disc. The pad pattern is much less common. Fewer choices in makes and about double the money for pads. Of course they are much larger also so they should wear better. Best price I found was $793.
The mini kit uses an 11.75" rotor and the forged dynapro calipers. Again, lots of pad choices. Uses a different hold down for the pads, clips not pins. 4 piston caliper. This one uses a radial mount where the honda kits are lug. I'm guessing lug is easier to DIY but the cardomain link the guy used this mini kit up front. Much higher end beefier caliper than the dynalite. Didn't price this one where I found great pricing but it's about $100 more than the 6 piston pricing them through summit.
That 6 piston set up is sexy as hell. The 4 piston is pretty practical. The 11" two piece rotors are pretty light and the calipers are a huge weight drop. There are fewer rotor options in the smaller bolt pattern used on the hat for 11" rotors compared to the 8x7 pattern used on the 11.75s.
Rotors in the kit numbers I listed are solid, not drilled or slotted. They have other kit numbers for those. The Calipers are black but can be done red with another number.